1. Field of the Invention
The present invention pertains to heated humidifiers, and in particular, to heated humidifiers with water chambers.
2. Description of the Related Art
Many individuals suffer from sleep apnea and other related diseases which result in episodic upper airway obstruction during sleep. As a consequence, there is repeated interruption of sleep in the patient. Positive airway pressure (PAP) devices have been developed to treat this disorder. A typical PAP device comprises a flow generator (e.g., a blower) that delivers gas via a delivery conduit to a user interface, such as a mask. It is also known to deliver the PAP pressure as a continuous positive airway pressure (CPAP), a variable airway pressure, such as a bi-level pressure that varies with the patient's respiratory cycle, or an auto-titrating pressure that varies with the monitored condition of the patient. Pressure support therapies are also provided to treat other medical and respiratory disorders, such as Cheynes-Stokes respiration, congestive heart failure, and stroke.
Providing positive airway pressure to such patients is well known in the art. However, it has been found that using dry pressurized air is uncomfortable to the user. Over time, breathing such air will dry out the patient's throat, nasal passage, and mucus membranes resulting in discomfort and pain. In order to overcome this problem many ventilators include a humidifier to add water vapor to the air inhaled by the patient. One such device exemplary of the art is disclosed in U.S. Pat. No. 5,673,687 to Dobson et al. (“the '687 patent”). This device includes a ventilator, a passive humidifier, and a delivery conduit. The passive humidifier disclosed in this patent has a reservoir filled with water and a corresponding lid. The humidifier is connected between the outlet of the ventilator and the air delivery conduit. As the patient breaths, air is forced out of the ventilator and passes over water contained in the reservoir. Water vapor is passively entrained with the dry air as the water naturally evaporates within the reservoir. The humidified air then passes through the delivery conduit and inhaled by the patient.
It was found desirable to increase the amount of water vapor entrained with the air. One such device capable of accomplishing this goal is the humidifier described in U.S. Pat. No. 6,349,722 to Gradon et al. The humidifier disclosed in this patent has a water chamber with a plastic top and a metal bottom. Forming the water chamber from two separate parts allows for easy access to the interior of the chamber and cleaning. The chamber sits on top of a heater plate. Active humidification occurs as the temperature of the heater plate increases above ambient temperature. The heat generated by the heater plate raises the temperature of the water contained in the chamber and thus accelerates the rate of evaporation. Aluminum is often used to form the metal bottom because of its low cost, and high thermal conductivity. The metal bottom is typically formed by stamping a sheet of aluminum. A rubber seal is then overmolded about the metal bottom in order to create a fluid tight seal with the plastic top.
Although such devices have advanced the art, several improvements can still be made. In the case of an aluminum metal bottom, it can become dinged and dented since the material has little shape memory. Secondly, the aluminum metal bottom is used in a humid environment and thus prone to corrosion and pitting. Careful application of anodizing or other similar processes is needed to control the degradation of the metal bottom. Another feature of these devices that could be improved upon is the manufacturing process. Typically, the metal bottom is formed by stamping and cutting a sheet of aluminum. Next, a fluid-tight seal is formed between the metal bottom and the plastic top by overmolding a seal about the metal bottom. The metal bottom is formed by stamping and cutting thin sheet aluminum in multiple steps using a progressive die. The part is then transferred to a second machine for overmolding the seal. This is a time consuming processing method and requires expertise in two very different manufacturing technologies.